Records of the Western Australian Museum 18: 263-276 (1997). 
A new species of pliosaurid reptile from the Early Cretaceous Birdrong 
Sandstone of Western Australia 
Arthur R. I. Cruickshank 1 and John A. Long 2 
1 Earth Sciences Section, Leicestershire Museums, Arts and Records Service, The Rowans, 
College Street, Leicester LE2 OJJ, U.K. 
2 Department of Earth and Planetary Sciences, Western Australian Museum, Francis Street, 
Perth, Western Australia 6000, Australia 
Abstract - Of three partial skeletons of small pliosauroid plesiosaurs from 
near Kalbarri in the Carnarvon Basin, Western Australia, two are described 
as Leptocleidus clemai sp. nov. The third is indeterminate. These constitute the 
first associated partial skeletons of Mesozoic reptiles recovered from Western 
Australia, and the first named species of fossil reptile from the State 
(excluding footprint inchnotaxa). They came from the (upper) glauconitic 
facies of the Birdrong Sandstone, a late Hauterivian-Barremian (Early 
Cretaceous) transgressive unit representing a nearshore shallow-marine 
episode of deposition. Fossil wood associated with the pliosaurs contains 
fossil pholadid bivalve borings and hyphae of saprophytic fungi. Leptocleidus 
is a small-sized (ca 3 m) genus of pliosauroid plesiosaur which is known 
from 'Wealden' deposits in England, South Africa and Australia. It retains 
many characters seen in Rhomaleosaurus, a pliosauroid of the English Lias 
(Hettangian -Toarcian; Early Jurassic). The new species Leptocleidus clemai sp. 
nov. is characterised by being the largest of the known species. Characters of 
the genus Leptocleidus are discussed. A brief review of the distribution of 
pliosauroids in time shows that the large, open-water, sarcophagous forms 
appear to have died out at the end of the Turonian and are replaced by the 
mosasaurs which first appear in the Cenomanian, leptocleidus- like forms 
seem to have been restricted to inshore habitats. 
INTRODUCTION 
Pliosauroid plesiosaurs are a characteristic 
component of many marine faunas throughout the 
Mesozoic (Brown 1981; Taylor 1992; Cruickshank 
1994, 1996a). They represent the top predators of 
the time and grew to over 14 m in length 
(Kronosaurus, Albian of Queensland). The 
contrasting plesiosauroids could also grow to 
extreme lengths, but they were not adapted for the 
role of sarcophagous predators, being instead 
pursuers of soft-bodied, or lightly armoured, small 
prey species (Brown 1981; Massare 1987; 
Cruickshank and Fordyce, in prep.). The 
morphological contrast between the superfamilies 
Pliosauroidea and Plesiosauroidea involves 
differences in the relative size of their heads, and 
length of their necks; pliosaurs having relatively 
large heads and short necks (Tarlo 1960; Taylor 
1992; Cruickshank 1994). The morphology of the 
body and limbs seems not to have varied 
significantly between plesiosaur and pliosaur, and 
they all adopted a form of underwater flight as 
their main form of propulsion (Storrs 1993; Riess 
and Frey 1991). 
Evolutionary trends in the Plesiosauria have been 
well documented by Brown (1981), and within the 
Pliosauroidea there is a conventional view of a 
general increase in body size through time, a 
relative increase in head length at the expense of 
neck length, and an overall decrease in both the 
number of neck vertebrae and the length of 
individual centra (Brown 1981; Tarlo 1960). 
However Leptocleidus-hke pliosauroids seem not to 
follow these trends, and keep a neck vertebral 
count of near 30, do not reduce the lengths of the 
centra, and have a small body size (ca 3 m). Much 
of their anatomy is very close to that of the genus 
Rhomaleosaurus, the 5.0 m long top predator of the 
European Lias (Early Jurassic) (Taylor 1992; 
Cruickshank, 1996a). 
Plesiosaurians have been known from Australia 
for a number of years (Molnar 1991), but the record 
in Western Australia is not so complete (e.g., 
Teichert and Matheson 1944; Long 1993) and the 
material reported here adds significantly to the 
knowledge of distribution of these animals in the 
Australian Cretaceous. Over several collecting 
expeditions from late 1992 to 1994, sponsored by 
Mr John Clema and Forrestania Gold Pty Ltd, the 
remains of three pliosauroid plesiosaurs were 
